Network Time Protocol (NTP) Project.
- The official page for the NTP Project. Contains information about the project, reference implementations of the protocol and software links. Also links to the pool of public NTP servers.

PresenTense Time Server
- Windows time server which synchronizes itself with any true time source, including GPS via rs-232 com ports and then acts as a time server for all network clients. Screen-shots, features list, documentation, and free 30-day demo version.